The invention is directed to an earth working, mining, or construction bit, and more particularly, to a cutting bit designed to be held in a mounting block that is affixed to a movable member.
Rotatable cutting bits held within a mounting block affixed to a movable member, such as a mining wheel or road planing drum, have been utilized to perform various excavating operations. These excavating operations can include applications relating to the removal of minerals as well as applications relating to road planing, trenching, concrete cutting and other construction applications. While earlier devices have performed satisfactorily, certain problems or drawbacks have existed, and the present invention is an improved design directed to successfully overcoming these drawbacks.
Typical cutting bits that have been previously utilized have included an enlarged diameter portion or a sharp stepped or flanged diameter portion at the rear end of the shank such as those illustrated in U.S. Pat. No. 4,201,421 to Den Besten et al. or in U.S. Pat. No. 3,519,309 to Engle et al., for example. In manufacturing the rearward portion of the bit body via techniques such as cold heading, forging or machining, it has been found that it is more economical to avoid forming such an enlarged diameter portion. It would thus be advantageous to provide a cutting bit wherein the rearward portion of the bit body is of a substantially constant diameter thereby eliminating an enlarged or sharp stepped diameter portion.
In previous cutting bits having such enlarged or sharply stepped diameter portions, it has been found that when the bit is extracted from the block, the sleeve can become positioned between the enlarged or stepped diameter portion and the cylindrical bore wall wedging the sleeve into the bore making it virtually impossible to easily extract the bit from the block and usually requiring the block to be removed and replaced. As can be appreciated, undesirable additional expense is associated with removing and then replacing the block resulting in unnecessary and expensive down time.
Earlier cutting bits have utilized the enlarged diameter or sharply stepped rearward portion of the bit as an abutment to retain a cylindrical retainer or clip captive on the bit. In operation of the previous bits and retainers, the rearward portion of the bit contacts the cylindrical wall of the bore so that wear on certain portions of the bore occurs as the bit rotates in the mounting block. It would thus be advantageous to provide a retainer wear sleeve which protects the bore of the block from wear due to contact with the shank of the cutting bit during operation. Such a retainer wear sleeve would increase the life of the block since contact between the shank and the bore of the block would be reduced.
During the cutting operation, a large volume of particulate materials are generated. These particulates tend to infiltrate the bore of the block-bit assembly, and collect in the volume between the rear shank and retainer wear sleeve. Earlier cutting bits having an enlarged diameter or sharply stepped rearward portion have trapped these contaminants and impaired the ability of the bit either to rotate in the bore of or to be efficiently removed from the block. Consequently, it would be advantageous to provide a cutting bit that does not have an enlarged diameter or sharply stepped rearward portion so that the tendency of particulate material being trapped between the sleeve and the shank is reduced.
In order to insert previous cutting bits having the enlarged diameter or sharply stepped rearward portion into the bore of the block, the rearward portion is aligned with the bore of the block and the bit driven into the bore. Earlier retainers for cutting bits have not provided any means to assist in guiding the bit into the bore of the mounting block. It would thus be advantageous if a retainer for a cutting bit did provide a means for guiding the bit into the bore and also protected the bore of the block from wear or distortion.